Further investigation of auroral roar fine structure

Received June 10, 1997; revised September 29, 1997; accepted October 28, 1997

Abstract:

In April 1996, a downconverting receiver was operated in Churchill,
Manitoba, Canada, to increase the statistics about the recently discovered
fine structure of auroral roar emissions. Auroral roar is found to be both
structured and unstructured. A wide variety of previously unknown tonal
features drifting in a complicated manner were recorded. These structured
features can be classified according to their duration, frequency drift,
and grouping with like features. Typically, 95% of the structured features
last less than 1 s. The slope of drifting features is more commonly
negative than positive with a magnitude typically less than a few kHz
s and a maximum of ~800 kHz s. The minimum bandwidth of
features is 6 Hz or less, and typical separation between similar features
is ~400 Hz. These measurements form a basis for reviewing proposed
generation mechanisms of auroral roar including a localized source model
and laser cavity mechanism.